1. Field of the Invention
The present invention relates to an improvement on a metal gasket which is suitable for preventing a fluid from leaking in a vacuum equipment employed for semiconductor manufacturing equipment, nuclear equipment, and the like.
2. Description of the Related Art
Conventionally, a rubber gasket has been generally employed as a sealant for a connecting portion in piping or a valve, a lid of a vacuum chamber, a reaction vessel for semiconductor manufacturing, or the like.
For a portion at a high temperature (200° C. or more) at which rubber gasket cannot be used or a portion which is in contact with a fluid which deteriorated rubber, a metal gasket for example such as a metal O-ring, a spring-inserted metal C-ring, knife-edge type metal gasket, or the like is employed.
The above-described metal gaskets are not necessarily able to cope with use conditions described below.
(a) In the case where the distance between flanges changes when in use, for example, in the case where the distance between flanges changes due to thermal expansion, applied pressure, vibration, or the like, such change cannot be followed, thereby causing the inability of sealing.
(b) In the case where a portion such as a lid of a reaction vessel or a gate valve on which opening and closing is repeated is sealed, for example a metal O-ring is crushed after being used once and cannot be used repeatedly.
(c) When a conventional metal gasket is used, it is not possible to increase a tightening load by structurally making the thickness of a flange thicker, making the diameter of a bolt increased, making the number of bolts increased, or the like.
(d) The material of a flange portion is soft such as aluminum and the like, so that there is a risk that a scar is formed on the flange portion when the tightening load is increased.
(e) Although a spring-inserted metal C-ring has a large elastic recovery amount, can be used repeatedly, and can follow the change in the distance between flanges to some extent, it is expensive.